480V to 240V Transformer

[kurt.brinker]

new guy here with an, judging fromt the other posts i have read, easy question.

My electrical history is limited. I worked on the electrical systems of the huey and cobra helicopter in the marines but now i am working as a PLC tech in the modern industry and i am somewhat the quasi electrician here. I am comfortable with household wiring, installing 480V motors and vfd's among other things. The ground i have yet to tread is transformers. I am installing a 3 phase transformer. 480V in and 120/240 out. i will get some more information for you momentarily but where can i start as far as connections go? From what i am told, i need a single leg of 240V out.


Back with the new info. It is an ACME Transformer Cat. No. T-3-53341-1S

I found this diagram as well. Is this correct?

I am thinking it should be wired like this.

L1-H1-1
L2-H2-1
L3-H3-1

Then X1, X2, and X3 are my three phases of 240? Each one will give me 240 to ground?

To take this even further, I am going into a VFD after the transformer to give me 220V 50Hz. The VFD accepts single or three phase 240. I am guessing thats 2 or 3 legs of 120?

 

[beanland]

Xfmr

Xfmr

The diagram if for 480V delta to 240/120 delta. The X4 is normally grounded and called the neutral. X1-X4-X2 give you 120/240V single phase. X1-X2-X3 give you 240V 3-phase. X3-X4 is only 208V.

 

[kurt.brinker]

ok so for my 240V 3 phase vfd input i would wire in X1-X2-X3? I thought 3 phase 240 was 3 legs of 120?

one more thing. along with the motor, i need to wire in a 220V power strip for foreign power. like this

how are those wired?

 

[mivey]

The high-side connection would be correct if you have 480 volts. The other taps can compensate for low highside voltage.

It would appear that this is a transformer that would normally provide 120/240 (120 volts to ground, 240 volts phase to phase). The X4 would be the neutral/ground with 120 volts at X1-X4/gnd and X2-X4/gnd, 240 volts at X1-X2, X2-X3, and X1-X3. If you had a transformer with changeable taps, you could parallel the secondaries and get 240 to ground (are you sure you need this?)

I suspect what you need is either one leg of the 120/240 volt configuration (240 volts phase-phase) or all three (240 volt 3 phase). You would have one high leg (208 volts to ground), and two 120 volt-to-ground legs. The 3 phase connection would be the most efficient use of the transformer.

 

[mivey]

X1-X2-X3 is correct. 3 phase 240 volts is 3 legs of 240 volts. I ASSUME they are wired the same way we wire 120 volt strips since they use 240 like we use 120.

 

[kurt.brinker]

let me give you a little more info.

i need the transformer because we have some equipment that runs on 220V 50hz. They were running it at 240V,60Hz with this transformer but they were using it as a steup up transformer. i have no idea how it was wired. they had it plugged into a 120 outlet and it was giving them 240V. I am using the transformer to go from 480V 3 phase and then into a VFD that i will set for 220V/50Hz. does that make sense?

 

[kurt.brinker]

The diagram if for 480V delta to 240/120 delta. The X4 is normally grounded and called the neutral. X1-X4-X2 give you 120/240V single phase. X1-X2-X3 give you 240V 3-phase. X3-X4 is only 208V.

they decided they only needed single phase 240. you say it is X1-X4-X2
how exactly does that work?

i need single phase 240 to power the plug i listed earlier.

i got 120V from X1 to X4 and i go 120 from X2 to X4. but i got 140 from X1 to ground and 140 from X2 to ground. I am guessing i need to place X1 and X2 as my L1 and L2 on the vfd. even though its 140 to ground, its 240 phase to phase so i am ok?

 

[beanland]

120v-n-120v

120v-n-120v

If you only need 120/240V single-phase, there is no reason to pay for and install the 3-phase transformer. Connect 480V 2-wire to a 480-120/240V single-phase transformer.

Warning: a VFD will generate "50Hz" for a motor but it will be all chopped up and distorted, not a neat sine-wave. If they need 220V 50Hz, a VFD may not be the best choice, if they need it to be clean. You may need to install an output filter on the VFD to clean up the waveform to get it close to sinusoidal.

Many electronic devices have "universal" power supplies that accept 90-245V and 25-60Hz. Is there a different power supply available for the device they are powering?

 

[iwire]

The couple of times I have been involved with providing 50 Hz it was with a motor generator set.

 

[coulter]

Curiousity question:
Has anyone looked into a UPS with a 60hz front end and a 50hz output?

carl

 

[beanland]

UPS - Great Option

UPS - Great Option

Since a full-conversion UPS goes from AC-DC-AC, it would be a great approach for a small load. I know they also make UPS's that will change voltage. Perhaps there is a 120VAC 60Hz input to 220V 50Hz output UPS out there.

 

[beanland]

UPS's

UPS's

I did find the Emerson and Liebert make 60Hz input - 50Hz output UPS. Add a 120V - 220V transformer at the output and you are in business.

 

[kurt.brinker]

If you only need 120/240V single-phase, there is no reason to pay for and install the 3-phase transformer. Connect 480V 2-wire to a 480-120/240V single-phase transformer.

Warning: a VFD will generate "50Hz" for a motor but it will be all chopped up and distorted, not a neat sine-wave. If they need 220V 50Hz, a VFD may not be the best choice, if they need it to be clean. You may need to install an output filter on the VFD to clean up the waveform to get it close to sinusoidal.

Many electronic devices have "universal" power supplies that accept 90-245V and 25-60Hz. Is there a different power supply available for the device they are powering?

the transformer was an extra so thats why we are using it.

i didn't know that about the vfd's.
i was wrong about the motor. The reason i switched from needing 3 phase 240 to single phase was because i discovered there was no motor, just some equipment that needed 240/50hz. (I am getting bits and pieces as the day moves along) the equipment is a flowmeter and a basic plc that collects data from a few pressure transducers and then outputs it to a program via rs-232.

I just used 2 legs from the transformer and got my 240 phase to phase. i put that into the vfd and set the parameters. i connected the power strip and plugged everything in. it all powered up just fine but they aren't going to check it out until tommorow.



should i just forget the VFD? slap in a terminal strip and run the power from the transformer straight to the power strip. (through a cb of course.)

 

[zog]

That wont work if you need 50Hz, and you cant run 50hZ through a 60Hz rated transformer.

 

[beanland]

Transformer

Transformer

You raise a good point. The Volt/Hz rating of the transformer should not be exceeded or you risk putting the transformer into saturation.

You could get a 50Hz rated transformer, they are widely available. Square D makes them.

Many transformers are dual rated 50Hz/60Hz.

If you get a transformer with taps, 120V/60Hz = 100V/50Hz. A transformer with a 100V tap, rated 120V @ 60Hz, and with the correct high voltage tap would function within its ratings.

 

[kurt.brinker]

That wont work if you need 50Hz, and you cant run 50hZ through a 60Hz rated transformer.

the vfd is post transformer. its 480/60hz going to 240/60hz and then into t avfd that drops it to 50hz. apparently they have been running everything on 60hz the past year with no problems so i am going to pull the vfd and put a terminal strip in.

 

[mistermudd]

This is how understand an ungrounded delta. A artificial ground tends to exist in the center of the delta. Potential between each phase and the so called ground when balanced will equal line voltage divided by the square root of 3 (your 140 volts). But with unbalanced phases this artificial ground will float. I do not think you want an ungrounded system (only code compliant under certain circumstances & your system will not be balanced). This is a separately derived system and must follow NEC 250.30 using X-4 to establish the new ground. At this point you will have 240 volts between X1, X2 & X3(Single phase 240 volts would be X1 to X2 or X2 to X3 or X3 to X1). Notice that you are using the entire winding in this case. 120 volts between X1, X4 & X4, X2 using only half of a winding. You will also have a ?high leg? of something over 240 volts between X3 & X4.

Disclaimer: I am not responsible if you let the smoke out of this thing.

Good luck.

 

[mivey]

The high leg should be 208 volts.

Could he corner ground to get 240 line to ground?

 

[kurt.brinker]

This is how understand an ungrounded delta. A artificial ground tends to exist in the center of the delta. Potential between each phase and the so called ground when balanced will equal line voltage divided by the square root of 3 (your 140 volts). But with unbalanced phases this artificial ground will float. I do not think you want an ungrounded system (only code compliant under certain circumstances & your system will not be balanced). This is a separately derived system and must follow NEC 250.30 using X-4 to establish the new ground. At this point you will have 240 volts between X1, X2 & X3(Single phase 240 volts would be X1 to X2 or X2 to X3 or X3 to X1). Notice that you are using the entire winding in this case. 120 volts between X1, X4 & X4, X2 using only half of a winding. You will also have a “high leg” of something over 240 volts between X3 & X4.

Disclaimer: I am not responsible if you let the smoke out of this thing.

Good luck.

i try my best to keep the ghosts inside.

are you saying i should ground X4 to the case with the rest of the grounds? right now my 480 ground goes to the case and the vfd is also grounded to the case. forget VFD now. i just want 240V single phase from this transformer to power my power strip. i am thinking X1 on one leg and X2 on the other leg with a ground that goes to the case of the xformer. yes/no?

 

[mistermudd]

IMO the secondary needs to be grounded. Whether at a corner or at the mid-point of a winding(if you may need 120). Otherwise the unbalance you are going to create is going to make this thing do some funny stuff. What are you connecting to the secondary of this transformer??? Should have a disconnect or panel according to the transformer tap rules in NEC 240. And yes you would install a system bonding jumper either at the transformer or disconnect that would bond X4 to the chassis, grounding electrode & neutral. There are alot of rules for seperatley derived systems make sure you bone up on them.